1. Field of the Invention
The present invention relates to ball grid array packages, more particularly, to an apparatus and method for reworking ball grid array packages.
2. Background
Ball Grid Array (BGA) packages reduce semi conductor package size and pin-to-pin trace gap by integrating more functions and reliability in a single chip. BGA technology is a cross between a pin grid array and a surface mount device. It is similar to a pin grid array except that solder balls attached to a land on the package replace pins. Input/Output (I/O) counts range from 16 to 2400, with the most common falling between 200 and 500 pins. The absence of leads makes the BGA a robust packaging option, which increases manufacturing yield.
BGA packages typically have solder ball-attachment problems due to manufacturing defect, improper end user handling or PCB reclaim processes. Since BGA packages are expensive to discard or replace, there has been an increasing demand for reworking (also referred to herein as xe2x80x9cReballingxe2x80x9d) damaged BGA packages.
Although BGA packages are extensively used, conventional techniques use inefficient reworking tools and procedures to rework damaged BGA packages.
One such technique is disclosed in U.S. Pat. No. 5,392,980 (Swamy et al). In Swamy et al:
xe2x80x9cThe process uses a rework tool which comprises a plate including one or more depressions corresponding to the contours of inverted BGA packages. A BGA package to be reworked is placed in a respective depression with what remains of the original solder ball grid facing upward. The residual solder balls are wicked away, thus leaving the BGA package with the pads that the solder balls were attached to being exposed. A stencil with BGA patterns punched into it is then placed over the rework tool and solder paste is screened onto the rework tool so that the solder is deposited on the BGA pads via the openings in the stencil.xe2x80x9d [U.S. Pat. No. 5,392,980, Abstract]
The techniques disclosed in Swamy et al has disadvantages. For example, solder pastes if not evenly spread affects the quality of the BGA package. Also, the technique does not allow reworking of BGA packages with damaged or defective solder balls.
Yet another common technique used for reworking BGA packages is to cover the BGA package with a stencil having a hole pattern similar to the BGA solder ball pattern. Thereafter, solder balls are manually poured on the stencils so that solder balls drop on the BGA package.
This technique also has disadvantages because manually pouring of solder balls may result in loss of solder balls. Also, manually pouring solder balls is labor intensive.
Therefore, there is need for a method and system for efficiently reworking BGA packages.
In one aspect of the present invention, an apparatus for reworking a BGA package is provided. The apparatus includes a housing with a solder ball compartment that includes solder balls; a sliding base plate positioned to slide under the solder ball compartment; and a BGA nest for supporting the BGA package and a stencil with a hole pattern similar to a solder ball pattern on the BGA package.
The sliding base plate has a BGA nest holder (at least one depression) adapted to receive the BGA nest with the BGA package and the stencil.
The housing includes a solder base plate that is moved in a first direction by the sliding base plate when the sliding base plate moves underneath the solder base plate in the first direction. The sliding base plate with the BGA nest, BGA package and the stencil is aligned with the solder ball compartment such that solder balls are placed on the BGA package through the stencil hole pattern. After the solder balls are placed on the BGA package, the sliding plate with the BGA package and the solder balls move in a second direction away from the solder ball compartment.
In another aspect of the present invention, a method for reworking a BGA package is provided. The method includes placing the BGA package in the BGA nest; covering the BGA package with the stencil having a hole pattern similar to the solder ball pattern of the BGA package; placing the BGA nest with the BGA package and the stencil in the nest holder; moving the nest holder with the BGA nest, BGA package and the stencil in the first direction underneath the solder ball compartment; and placing solder balls from the solder ball compartment on the BGA package through the hole pattern of the stencil. Thereafter, withdrawing the sliding base plate in the second direction away from the solder base compartment after solder balls are placed on the BGA package.
In one aspect of the present invention, solder balls are not wasted or lost because they are contained in the solder ball compartment.
In another aspect of the present invention, moving the sliding plate is not labor intensive and hence rework of the BGA package is performed efficiently.
This summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiments thereof concerning the attached drawings.